1. Field of Invention
The present invention relates, generally, to ablation instrument systems that use ablative energy to ablate internal bodily tissues. More particularly, to preformed guide apparatus which cooperate with energy delivery arrangements to direct the ablative energy in selected directions along the guide apparatus.
2. Description of the Prior Art
It is well documented that atrial fibrillation, either alone or as a consequence of other cardiac disease, continues to persist as the most common cardiac arrhythmia. According to recent estimates, more than two million people in the U.S. suffer from this common arrhythmia, roughly 0.15% to 1.0% of the population. Moreover, the prevalence of this cardiac disease increases with age, affecting nearly 8% to 17% of those over 60 years of age.
Atrial arrhythmia may be treated using several methods. Pharmacological treatment of atrial fibrillation, for example, is initially the preferred approach, first to maintain normal sinus rhythm, or secondly to decrease the ventricular response rate. Other forms of treatment include drug therapies, electrical cardioversion, and RF catheter ablation of selected areas determined by mapping. In the more recent past, other surgical procedures have been developed for atrial fibrillation, including left atrial isolation, transvenous catheter or cryosurgical ablation of His bundle, and the Corridor procedure, which have effectively eliminated irregular ventricular rhythm. However, these procedures have for the most part failed to restore normal cardiac hemodynamics, or alleviate the patient""s vulnerability to thromboembolism because the atria are allowed to continue to fibrillate. Accordingly, a more effective surgical treatment was required to cure medically refractory atrial fibrillation of the Heart.
On the basis of electrophysiologic mapping of the atria and identification of macroreentrant circuits, a surgical approach was developed which effectively creates an electrical maze in the atrium (i.e., the MAZE procedure) and precludes the ability of the atria to fibrillate. Briefly, in the procedure commonly referred to as the MAZE III procedure, strategic atrial incisions are performed to prevent atrial reentry circuits and allow sinus impulses to activate the entire atrial myocardium, thereby preserving atrial transport function postoperatively. Since atrial fibrillation is characterized by the presence of multiple macroreentrant circuits that are fleeting in nature and can occur anywhere in the atria, it is prudent to interrupt all of the potential pathways for atrial macroreentrant circuits. These circuits, incidentally, have been identified by intraoperative mapping both experimentally and clinically in patients.
Generally, this procedure includes the excision of both atrial appendages, and the electrical isolation of the pulmonary veins. Further, strategically placed atrial incisions not only interrupt the conduction routes of the common reentrant circuits, but they also direct the sinus impulse from the sinoatrial node to the atrioventricular node along a specified route. In essence, the entire atrial myocardium, with the exception of the atrial appendages and the pulmonary veins, is electrically activated by providing for multiple blind alleys off the main conduction route between the sinoatrial node to the atrioventricular node. Atrial transport function is thus preserved postoperatively as generally set forth in the series of articles: Cox, Schuessler, Boineau, Canavan, Cain, Lindsay, Stone, Smith, Corr, Change, and D""Agostino, Jr., The Surgical Treatment Atrial Fibrillation (pts. 1-4), 101 THORAC CARDIOVASC SURG., 402-426, 569-592 (1991).
While this MAZE III procedure has proven effective in ablating medically refractory atrial fibrillation and associated detrimental sequelae, this operational procedure is traumatic to the patient since this is an open-heart procedure and substantial incisions are introduced into the interior chambers of the Heart. Consequently, other techniques have been developed to interrupt atrial fibrillation restore sinus rhythm. One such technique is strategic ablation of the atrial tissues through ablation catheters.
Most approved ablation catheter systems now utilize radio frequency (RF) energy as the ablating energy source. Accordingly, a variety of RF based catheters and power supplies are currently available to electrophysiologists. However, radio frequency energy has several limitations including the rapid dissipation of energy in surface tissues resulting in shallow xe2x80x9cburnsxe2x80x9d and failure to access deeper arrhythmic tissues. Another limitation of RF ablation catheters is the risk of clot formation on the energy emitting electrodes. Such clots have an associated danger of causing potentially lethal strokes in the event that a clot is dislodged from the catheter. It is also very difficult to create continuous long lesions with RF ablation instruments.
As such, catheters which utilize other energy sources as the ablation energy source, for example in the microwave frequency range, are currently being developed. Microwave frequency energy, for example, has long been recognized as an effective energy source for heating biological tissues and has seen use in such hyperthermia applications as cancer treatment and preheating of blood prior to infusions. Accordingly, in view of the drawbacks of the traditional catheter ablation techniques, there has recently been a great deal of interest in using microwave energy as an ablation energy source. The advantage of microwave energy is that it is much easier to control and safer than direct current applications and it is capable of generating substantially larger and longer lesions than RF catheters, which greatly simplifies the actual ablation procedures. Such microwave ablation systems are described in the U.S. Pat. No. 4,641,649 to Walinsky; U.S. Pat. No. 5,246,438 to Langberg; U.S. Pat. No. 5,405,346 to Grundy, et al.; and U.S. Pat. No. 5,314,466 to Stern, et al, each of which is incorporated herein by reference.
Most of the existing microwave ablation catheters contemplate the use of longitudinally extending helical antenna coils that direct the electromagnetic energy in all radial directions that are generally perpendicular to the longitudinal axis of the catheter. Although such catheter designs work well for a number of applications, such radial output is inappropriate when the energy needs to be directed toward the tissue to ablate only.
Consequently, microwave ablation instruments have recently been developed which incorporate microwave antennas having directional reflectors. Typically, a tapered directional reflector is positioned peripherally around the microwave antenna to direct the waves toward and out of a window portion of the antenna assembly. These ablation instruments, thus, are capable of effectively transmitting electromagnetic energy in a more specific direction. For example, the electromagnetic energy may be transmitted generally perpendicular to the longitudinal axis of the catheter but constrained to a selected radial region of the antenna, or directly out the distal end of the instrument. Typical of these designs are described in the U.S. patent application Ser. No. 09/178,066, filed Oct. 23, 1998; and Ser. No. 09/333,747, filed Jun. 14, 1999, each of which is incorporated herein by reference.
In these designs, the resonance frequency of the microwave antenna is preferably tuned assuming contact between the targeted tissue or blood and a contact region of the antenna assembly extending longitudinally adjacent to the antenna longitudinal axis. Hence, should a portion of, or substantially all of, the exposed contact region of the antenna not be in contact with the targeted tissue or blood during ablation, the resonance frequency will be adversely changed and the antenna will be untuned. As a result, the portion of the antenna not in contact with the targeted tissue or blood will radiate the electromagnetic radiation into the surrounding air. The efficiency of the energy delivery into the tissue will consequently decrease which in turn causes the penetration depth of the lesion to decrease.
This is particularly problematic when the microwave antenna is not in the blood pool, or when the tissue surfaces are substantially curvilinear, or when the targeted tissue for ablation is difficult to access, such as in the interior chambers of the Heart. Since these antenna designs are generally relatively rigid, it is often difficult to maneuver substantially all of the exposed contact region of the antenna into abutting contact against the targeted tissue. In these instances, several ablation instruments, having antennas of varying length and shape, may be necessary to complete just one series of ablations.
Accordingly, a system for ablating a selected portion of a contact surface of biological tissue is provided. The system is particularly suitable to ablate cardiac tissue, and includes an elongated ablation sheath having a preformed shape adapted to substantially conform a predetermined surface thereof with the contact surface of the tissue. The ablation sheath defines an ablation lumen extending therethrough along an ablation path proximate to the predetermined surface. An elongated ablative device includes a flexible ablation element which cooperate with an ablative energy source which is sufficiently strong for tissue ablation. The ablative device is formed and dimensioned for longitudinal sliding receipt through the ablation lumen of the ablation sheath for selective placement of the ablative device along the ablation path created by the ablation sheath. The ablation lumen and the ablative device cooperate to position the ablative device proximate to the ablation sheath predetermined surface for selective ablation of the selected portion.
Accordingly, the ablation sheath in its preshaped form functions as a guide device to guide the ablative device along the ablation path when the predetermined surface of the ablation sheath properly contacts the biological tissue. Further, the cooperation between the ablative device and the ablation lumen, as the ablative device is advanced through the lumen, positions the ablative device in a proper orientation to facilitate ablation of the targeted tissue during the advancement. Thus, once the ablation sheath is stationed relative the targeted contact surface, the ablative device can be easily advanced along the ablation path to generate the desired tissue ablations.
In one embodiment, the ablative device is a microwave antenna assembly which includes a flexible shield device coupled to the antenna substantially shield a surrounding area of the antenna from the electromagnetic field radially generated therefrom while permitting a majority of the field to be directed generally in a predetermined direction toward the ablation sheath predetermined surface. The microwave antenna assembly further includes a flexible insulator disposed between the shield device and the antenna. A window portion of the insulator is defined which enables transmission of the directed electromagnetic field in the predetermined direction toward the ablation sheath predetermined surface. The antenna, the shield device and the insulator are formed for manipulative bending thereof, as a unit, to one of a plurality of contact positions to generally conform the window portion to the ablation sheath predetermined surface as the insulator and antenna are advanced through the ablation lumen.
In another embodiment, to facilitate alignment of the ablative device assembly in the ablation lumen, the ablative device provides a key device which is slidably received in a mating slot portion of the ablation lumen. In still another embodiment, the system includes a guide sheath defining a guide lumen formed and dimensioned for sliding receipt of the ablation sheath therethrough. The guide sheath is pre-shaped to facilitate positioning of the ablation sheath toward the selected portion of the contact surface when the ablation sheath is advanced through guide lumen.
The ablation sheath includes a bendable shape retaining member extending longitudinally therethrough which is adapted to retain the preformed shape of the ablation sheath once positioned out of the guide lumen of the guide sheath.
The ablative energy is preferably provided by a microwave ablative device. Other suitable tissue ablation devices, however, include cryogenic, ultrasonic, laser and radiofrequency, to name a few.
In another aspect of the present invention, a method for treatment of a Heart includes forming a penetration through a muscular wall of the Heart into an interior chamber thereof; and positioning a distal end of an elongated ablation sheath through the penetration. The ablation sheath defines an ablation lumen extending along an ablation path therethrough. The method further includes contacting, or bringing close enough, a predetermined surface of the elongated ablation sheath with a first selected portion of an interior surface of the muscular wall; and passing a flexible ablative device through the ablation lumen of the ablation sheath for selective placement of the ablative device along the ablation path. Once these events have been performed, the method includes applying the ablative energy, using the ablative device and the ablation energy source, which is sufficiently strong to cause tissue ablation.
In one embodiment, the passing is performed by incrementally advancing the ablative device along a plurality of positions of the ablation path to produce a substantially continuous lesion. Before the positioning event, the method includes placing a distal end of a guide sheath through the penetration, and then positioning the distal end of the ablation sheath through the guide lumen of the guide sheath.
In still another embodiment, before the placing event, piercing the muscular wall with a piercing sheath. The piercing sheath defines a positioning passage extending therethrough, The placing the distal end of a guide sheath is performed by placing the guide sheath distal end through the positioning passage of the piercing sheath.
In yet another configuration, the positioning the distal end event includes advancing the ablation sheath toward the first selected portion of the interior surface of the muscular wall through a manipulation device extending through a second penetration into the Heart interior chamber independent from the first named penetration.
In another embodiment, a system for ablating tissue within a body of a patient is provided including an elongated rail device and an ablative device. The radial device is adapted to be positioned proximate and adjacent to a selected tissue region to be ablated within the body of the patient. The ablative device includes a receiving passage configured to slideably receive the rail device longitudinally therethrough. This enables the ablative device to be slideably positioned along the rail substantially adjacent to or in contact with the selected tissue region. The ablative device, having an energy delivery portion which is adapted to be coupled to an ablative energy source, can then be operated to ablate the selected tissue region.
In this configuration, the ablative device is adapted to directionally emit the ablative energy from the energy delivery portion. A key assembly cooperates between the ablative device and the rail member, thus, to properly align the directionally emitted ablative energy toward the tissue region to be ablated. This primarily performed by providing a rail device with a non-circular transverse cross-sectional dimension. The receiving passage of the ablative device further includes a substantially similarly shaped non-circular transverse cross-section dimension to enable sliding of the ablative device in a manner continuously aligning the directionally emitted ablative energy toward the tissue region to be ablated as the ablative device advances along the rail device.